Seroprevalence study of SARS-CoV-2 infection in General Practice in Ireland
There is much to learn about SARS-CoV-2 immunity, and serological testing may have a role in tracking viral spread and assessment of our public health efforts. General practice provides an established and accessible means to assess seroprevalence in communities and in at-risk groups.
This seroprevalence study utilised 2 manufacturers’ point-of-care (POCT) SARS-CoV-2 IgM-IgG combined antibody tests, offered to patients and healthcare workers in general practice. In addition to providing a serum or capillary blood sample, participants were asked whether they had experienced symptoms suggestive of COVID-19 since February 2020, and whether they had a previous polymerase chain reaction (PCR) test for SARS-CoV-2.
From June 15th to July 10th 2020, 971 participants from 15 general practices were tested. Seroprevalence was estimated at 12.9% in patients attending general practice, and 12.9% in staff working in general practice, with administrative staff having the lowest seroprevalence (6.5%) and nursing staff having the highest (16.3%). These rates are much higher than estimates for the national average (1.7%). Seroprevalence was similar in males and females; was lowest in those 65 years or older; and was elevated in those who had previous symptoms suggestive of SARS-CoV-2 or who had undergone a polymerase chain reaction (PCR) test for SARS-CoV-2 via nasal and throat swab. Sensitivity was 78% and 79% for each test kit type, giving a combined sensitivity of 82%. About a third (32%) of those patients with previous symptoms suggestive of SARS-CoV-2 had undergone a PCR test for SARS-CoV-2 and 17% of those who were seropositive reported no symptoms during the months preceding testing. Average length of time between participants testing positive for SARS-CoV-2 on laboratory PCR testing and testing positive for IgG antibodies was 83 days. Six patients with confirmed COVID-19 infection on PCR testing did not demonstrate presence of IgG antibodies.
While not proof of immunity and requiring further study, SARS-CoV-2 POC testing can establish serological prevalence in general practice settings, with a sensitivity of approximately 80%. Persistence of antibodies for an average of 12 weeks in four-fifths of participants with previous COVID-19 infection is encouraging as we learn more about the SARS-CoV-2 immune response.